A UNIX or Windows server with a DNS entry, smtp for outgoing email and one open and free incoming tcp port.
You must have administrative rights (UNIX: root) on this server and a basic understanding of UNIX and networking.

F*EX is written in Perl which does not have common security problems with buffer overruns, segmentation faults, heap and stack corruption.
F*EX does not use an extra web server or a (SQL) database, so no typical web attacks are possible.
F*EX was analyzed by security company revshell.com and labeled as "secure".
F*EX comes with source code, so everybody can verify it.